Technical Abstract:
In a previous study, three chromosomal regions which significantly affected backfat thickness in a Meishan-White composite resource population were reported. That study utilized data collected on more than 530 carcasses from backcross pigs (both Meishan and White composite sired pigs were represented). The chromosomal regions detected were 1:136-138, 7:40-60 and X:59-63 where the values are chromosome:relative position in cM. In the present study, phenotypic data for all of the animals included in the previous study, along with littermates which were retained for breeding (n=730 records), was analyzed. Traits studied were ultrasonic backfat measurements (first rib, last rib and last lumbar vertebra) and weights of pigs at 14 and 26 wk of age. The statistical analyses utilized a least- squares interval mapping procedure and F-ratios were converted to genome- wide significance levels. Fixed effects fitted were breed composition, sex and season of birth for the unadjusted model (UNA) and weight was included as a covariate in the adjusted model (ADJ; backfat measures only). The 1:136-138 region affected all measures of backfat at 14 and 26 wk and was most significant in the UNA model, as it also affected 14 and 26 wk weights. The 7:40-60 region was significant for all backfat measures at 14 and 26 wk in the ADJ model, and to a lesser degree for backfat at 26 wk in the UNA model. While 7:40-60 was not associated with 14 wk weights, it was associated with 26 wk weights. The X:59-63 affected all measures of backfat with similar significance levels for the UNA and ADJ models, but did not affect live weight.